I don't cold-condition my beers. I put them in a dark closet until they're ready to drink, and then refrigerate them. I usually let them sit at least three weeks before I drink them, but in the fridge, I can see that being longer, since the yeast (at least ale yeast) will have a harder time at those temperatures.

well, I also condition in my closet for about 3-4 weeks, but last time I think the fridge took away my carbonation, because after I took the bottles out of the fridge for a few days the beer bottles got hard again.

I'm no chemist, but I'm not sure that's possible. When your beer conditions in the closet, the yeast consume the sugar you added for priming, and the result is that a small amount of CO2 is created. If your caps are sealed tightly, I don't think the CO2 will disappear just because it's cold.

well, thats what I thought, but the beer was flat and I could press in teh sides to my plastic PET bottles. When I took the bottles out of the fridge for a few days/weeks the bottles got rock hard again.

The only other thing I can think of is I didnt let them carbonate long enough before putting them in the fridge the first time.

well, thats what I thought, but the beer was flat and I could press in teh sides to my plastic PET bottles. When I took the bottles out of the fridge for a few days/weeks the bottles got rock hard again.

The only other thing I can think of is I didnt let them carbonate long enough before putting them in the fridge the first time.

That is possible or more likely the carbonation dissolved in the cold beer. As the temperature of a liquid decreases it has a tendency to absorb more gasses. As the co2 is already in solution a cold beer will have a harder time releasing it until it warms up. (I'm a chemist btw.)

Another concern I've had is that the swirlling motion of the siphon isn't vigorous enough assure complete distribution of the sugar throughout the solution of beer. Could happen even though the laws of entropy assure even distribution eventually.
Try stirring the beer with a spoon (NO SPLASHING!) to assure even mixing.

That is possible or more likely the carbonation dissolved in the cold beer. As the temperature of a liquid decreases it has a tendency to absorb more gasses. As the co2 is already in solution a cold beer will have a harder time releasing it until it warms up. (I'm a chemist btw.)

Another concern I've had is that the swirlling motion of the siphon isn't vigorous enough assure complete distribution of the sugar throughout the solution of beer. Could happen even though the laws of entropy assure even distribution eventually.
Try stirring the beer with a spoon (NO SPLASHING!) to assure even mixing.

Hooray for chemists!

Question: why don't commercial beers tend to have the same problem when placed in a refrigerator?

Question: why don't commercial beers tend to have the same problem when placed in a refrigerator?

My guess would be that they aren't carbonated with yeast/sugar/fermentation but with CO2 by force. By the same logic cooling the beer while force carbonating would allow more gas to be dissolved in the beer while cold, saturated solution, and slight agitation, pouring, allows it to come out of solution easier, nucleation.

I let my beer bottle condition at room temperature for a few weeks before putting them in the fridge to chill for drinking, and then only chill what I'm going to be drinking for the next week or so. The hefe I recently brewed did the same thing; I put one bottled in plastic in the fridge 2 weeks after bottling, and it "lost" a good portion of the carbonation, despite the bottle being quite firm at room temp. However, the beer I put in the fridge a week later was perfectly carbed, even after several days of being chilled.